Handler的基本应用

朱雀 2022-07-16 08:50 143阅读 0赞

1.    handler用来更新UI，因为只能在UI线程里更新UI；

2.    handler是Android里的一种消息处理机制，可以发送和处理消息，也是一种更新UI的机制，最根本的是为了解决多线程并发的问题；

3.    handler更新UI的方法，使用post。

package com.example.kirito.myapplication;
    
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.os.Handler;
    import android.widget.TextView;
    
    /**
     * Created by kirito on 2016.10.12.
     */
    
    public class TestHandler extends Activity {
        private TextView tv;
        private Handler handler = new Handler();
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.testhandler);
    
            tv = (TextView) findViewById(R.id.tv_handler);
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    //使用post在Thread里更新UI（TextView）
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            tv.setText("update UI");
                        }
                    });
                }
            }).start();
        }
    }

4.使用handler.postDelay，实现图片的轮询切换。

package com.example.kirito.myapplication;
    
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.os.Handler;
    import android.widget.ImageView;
    import android.widget.TextView;
    
    /**
     * Created by kirito on 2016.10.12.
     */
    
    public class TestHandler extends Activity {
        private TextView tv;
        private Handler Myhandler = new Handler();
        private MyRunnable runnable = new MyRunnable();
        private ImageView iv;
        private int index = 0;
    
        private int images[] = {R.drawable.a,R.drawable.b,R.drawable.check};
    
        /**
         * 使用MyRunnable来轮询切换图片
         */
        private class MyRunnable implements Runnable{
            @Override
            public void run() {
                index++;
                index %= 3;
                iv.setImageResource(images[index]);
                //postDelayed是关键
                Myhandler.postDelayed(runnable,1000);
            }
        }
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.testhandler);
    
            iv = (ImageView) findViewById(R.id.iv_handler);
            //启动MyHandler
            Myhandler.postDelayed(runnable,1000);
        }
    }

5.使用handler的sendMessage方法来更新UI

package com.example.kirito.myapplication;
    
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.os.Handler;
    import android.os.Message;
    import android.widget.ImageView;
    import android.widget.TextView;
    
    /**
     * Created by kirito on 2016.10.12.
     */
    
    public class TestHandler extends Activity {
        private TextView tv;
        //使用handler的handleMessage更新UI
        private Handler Myhandler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                tv.setText(msg.arg1 + "");
            }
        };
        
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.testhandler);
            tv = (TextView) findViewById(R.id.tv_handler);
            new Thread(){
                @Override
                public void run() {
                    super.run();
                    Message msg = new Message();//使用Message的Object参数可以传递更多信息

//msg的生成可以使用handler的obtainMessage方法

msg.arg1 = 88; //handler发送消息 Myhandler.sendMessage(msg); \} \}.start(); \}\}

//移除运行的Runnable handler.removeCallbacks(runnable);

7.Handler添加CallBack拦截消息的传送

package com.example.kirito.myapplication;
    
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.os.Handler;
    import android.os.Message;
    import android.widget.ImageView;
    import android.widget.TextView;
    import android.widget.Toast;
    
    /**
     * Created by kirito on 2016.10.12.
     */
    
    public class TestHandler extends Activity {
        private TextView tv;
        //使用handler的handleMessage更新UI
        private Handler Myhandler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                tv.setText(msg.arg1);
            }
        };
    
        private Handler handler = new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                Toast.makeText(getApplicationContext(),"1.1",Toast.LENGTH_SHORT).show();
                return false;//若设置为true下面的hangdleMessage方法将不会执行，消息被截获
            }
        }){
            @Override
            public void handleMessage(Message msg) {
                Toast.makeText(getApplicationContext(),"1.2",Toast.LENGTH_SHORT).show();
            }
        };
        
        
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.testhandler);
            
            
            //发送一个空消息
            handler.sendEmptyMessage(1);
        }
    }